Wendy Zuckerman

And here was his life's work sitting in front of him in the form of a medical mystery.

He got in touch with Rosamund and said, would you mind if I look through your daughter's medical records?

And she was like, yes, go for it.

Handed them over and Stephen dove in.

Stephen also went to the hospital where sections of Ella's lungs were being preserved.

He pulled out these tiny lung scrapings that are about the size of a fingernail.

put them under the microscope, and straight away, he saw something odd.

The lining of her lungs, which should protect them from gunk in the air, had been totally destroyed.

In a healthy lung, you should see these lovely cells that look like columns with little hairs.

But with Ella, those little columns had been replaced by a totally different cell, one that pumps out mucus.

And this was mucking everything up.

You are supposed to have some mucus in your lungs, and it's helpful.

It captures gunk in the air and helps you to cough it out.

But Ella's lungs had become a bit like a mucus factory.

Stephen looked for signs of what might have been irritating her lungs so much, like a bacterial or fungal infection.

But nothing could explain this.

But then a new clue emerged, away from the lab.

Something that clinched it for him.

An air pollution station.

It was monitoring stuff like nitrogen dioxide, which gets spewed out by London traffic and can damage lung cells.